The present invention relates generally to so-called mechanical seals. More particularly, the invention concerns rotary end face seals, that is, seals in which the primary seal is usually formed between oppositely directed faces of two seal units lying in opposed relation and making contact along a seal band formed on or forming a part of the respective radial or end faces of the seal rings. Seals made according to the present invention are an improvement over known seals of a somewhat similar character, such as seals of the type shown and described in U.S. Pat. No. 3,241,843.
Seals of this type are sometimes referred to as heavy duty seals or grit seals, based on their well-known ability to be used in severe service environments. These seals are commonly used as seals for the track rollers or final drives of earth moving equipment in other track laying vehicles such as military tanks, or in other severe applications, such as in off-the-road scrapers, graders or other vehicles.
Seals such as those described and claimed in U.S. Pat. No. 3,241,843 have met with remarkable success by reason of their extreme reliability, and their ability to function as dirt excluders and lubricant retainers, even under extremely severe conditions.
By way of example, such seals routinely operate successfully in sand, water, mud, and rock and gravel environments, and in desert areas, in temperature climates, and in regions where the temperature is 20.degree. F. below zero or lower. Such seals perform their primary function of sealing under these conditions both because the end faces are precisely finished and because the seal rings themselves are accurately positioned and loaded by cooperating elastomeric rings of various configurations, with such rings also applying the desired range of loading forces, providing a secondary seal, and also providing sufficient driving torque so that relative rotation occurs only at the primary seal faces of the seal rings and not between the seal rings and the elastomer, or between the elastomer and a part of the machine housing. By "secondary seal" is meant any seal which is made between parts which do not undergo rotation relative to each other. Whereas seals of this type most commonly comprise an identical pair of seal rings and an identical pair of secondary sealing and driving members, arranged in mirror image relation, certain applications of these seals may be made where only one primary and one secondary member are used, with the mating surface being of some configuration other than that of the other parts of the seal assembly. The principles of the present invention are applicable to both types of seals.
As is often the case with seals of the type described above, in spite of the great success with the basic concept there is still the need for further improvements, particularly where the seals may be used in applications not originally envisaged by the designer.
Specifically, seals of the general type with which this invention is concerned are often used where lubricant is present only when parts associated with the seal undergo continuous motion, or where such parts are operated with reasonable frequency. By way of example, in final drive applications, a driving mechanism must be provided to transmit power from a transmission, differential, or similar assembly, to drive rollers or sprockets. In such cases, it is common for seals, and perhaps the bearings, to achieve lubrication by reason of splash action or flow caused by motion of the parts protected by the seal unit.
In the case of heavy duty vehicles such as military tanks, earth moving equipment or the like, it is not uncommon for the vehicle to be out of active use for extended periods, even where this is not economically desirable. For example, construction equipment is sometimes left unused for several months or more if weather prohibits construction operations. Moreover, considerable time elapses between the time an earth mover or other machine is taken out of service at one location and the time when it is placed in service in another location, or is undergoing repair for reasons other than those connected with repair of the sealed parts. In such cases, it has sometimes been found that seal damage, or even failure, occurs when there has been no movement of the sealed part for some time, during which lubrication to the seal is non-existent. Accordingly, upon start up, especially under extreme conditions, the seal may be damaged or its life shortened by lubrication failure occurring between the time the mechanism is operated and the seal can be properly lubricated by oil transferred thereto from or by other moving parts of the mechanism.
Because heavy duty seals of the type with which the present invention is concerned are designed for long life, they have customarily been formed with seal faces of considerable radial extent, such faces being finish ground so that, as wear occurs, the seal band moves progressively inwardly from the outermost periphery of the seal units to an area lying somewhat radially inwardly thereof. However, in most applications, by the time the seal band has moved inwardly a measurable amount, such as one-third or one-half of the radial extent of the seal face, the seal is generally ready to be discarded. The length of time to wear such a seal to this extent is usually several thousand hours or more, however, and the parts associated with the seal have by that time generally been worn out and discarded.
In view of the foregoing circumstances, it is an object of the present invention to provide a seal unit having an extended life in relation to similar but unimproved prior art seal.
Another object is to provide a heavy duty seal unit which includes a lubricant reservoir intended to eliminate or diminish the likelihood of dry starting after non-use of the mechanism for an extended time.
Another object is the provision of a heavy duty seal having fins, vanes or slots associated with the lubricant reservoir so as to insure distribution of the lubricant about the inner periphery of the end face of the seal upon initial start-up.
A further object is to provide a seal having a lubricant reservoir as well as means for creating turbulence within the reservoir upon relative rotation of the seal ring so as to facilitate lubricant circulation as well as increased heat transfer by the lubricant and the parts lubricated thereby.
A still further object is to provide a heavy duty grit seal having means for receiving and retaining a certain amount of lubricant during operation and for retaining at least a certain amount thereof in the region of the seal faces when rotation ceases, with such amount of lubricant being greatly increased relative to the merely incidental amounts of lubricant, if any, retained in this area by prior art seals.
Another object is to provide a primary seal ring having the characteristics referred to above and which is operable with various known types of secondary seal rings, including seal rings having parallelogram cross sections, generally equivalent cross sections, and those of quite different cross sections as well.
A further object is to provide an improved lubricant retaining seal which is especially useful in seals of mirror image or associated pair design, as well as with other designs.
These and other objects and advantages of the invention, including those inherent in the invention, are accomplished by providing a seal unit having at least one primary seal ring of a relatively rigid material, and at least one elastomeric or other flexible secondary seal ring associated with the ring in sealing and driving relation therewith, with the primary seal ring having a seat for the driving ring, a generally radially extending, axially directed, primary seal face, and means lying radially inwardly thereof and defining a reservoir for receiving lubricant, and, in some cases, ribs, vanes, or slots on the reservoir-defining surfaces of the primary seal ring to aid in lubricant transfer and to provide lubricant turbulence in use of the seal assembly.
The manner in which these and other of the objects of the invention are achieved will become more clearly apparent when reference is made to the accompanying detailed description of the invention set forth by way of example, and to the drawings, in which like reference numbers indicate corresponding parts throughout.